Hur Jun (Actor Kim Joo-hyuk)

Born from a concubine and the governor of Yongcheon, Euijoo. Hur Jun encounters a brilliant doctor () by the name of Yoo Eui-tae in Saneum. He finds work as a medicinal herb gatherer to start a new life. When Hur Jun witnesses Yoo Eui-tae save a dying person through medicine, he decides to become a doctor. Through the help of Ye-jin whom Hur Jun meets at Doctor Yoo's Oriental clinic, he is able to study rare medical texts imported from the Ming Empire. This enables him to expand his medical knowledge to the point where he can start treating patients. Hur Jun even missed taking an important state exam because of an emergency patient who needed immediate treatment to survive. Hur Jun returns to Yoo Eui-tae to learn more under his tutelage and together they cure many patients. But Hur Jun despairs that he cannot cure his mentor's stomach cancer.

Yoo Eui-tae (Actor Baek Yoon-shik)

A famous Oriental medicine doctor in Saneum who was regarded as the best. Not only was he a skilled doctor but he also had empathy () for his patients. He would suck out pus from sores, treat leper patients and would not shy away from any grotesque ailments. He only cared about the well-being of his patients. When Yoo sees that Hur Jun has become a healer who connects with his patients, he accepts him back at his clinic. After Yoo Eui-tae diagnoses himself with stomach cancer, he asks Hur Jun to dissect his body upon his death and use the knowledge he gleans from this to help future cancer patients.

Ye-jin (Actress Park Jin-hee)

Both of her parents died when she was young and so her father's friend Yoo Eui-tae stepped in and adopted her. Naturally smart with a warm heart, she is fully capable of becoming a doctor but in the male-dominated Joseon era, she was denied opportunities to advance. But one day she meets a young man with piercing eyes at the clinic and she stirs a passion within her. So she shares her knowledge of medicine with the young medicinal herb gatherer who aspires to become a doctor. She recommends essential medical texts and supports him to continue his career goals. Surviving the Japanese Invasion of Korea, she works as a royal nurse together with Dr. Hur Jun, who rises to the prestigious position of royal doctor, after they both spent many years healing commoners.